1. Field of the Invention
The present invention relates to an image capturing apparatus and, more particularly, to an image capturing apparatus which generates image data of a multi-channel image.
2. Description of the Related Art
A color image capturing apparatus such as a digital camera forms an object image via an imaging optical system on a capturing device having color filters arranged periodically, and generates digital image data by photoelectric conversion and analog-to-digital (AD) conversion. In general, color filters for three, R, G, and B colors are used. The sensitivity characteristic of the capturing device is uniform for all pixels. Color information for an obtained image is limited to these three colors, and even tone information is restricted to a range that is defined by the sensitivity characteristic of the capturing device.
When obtaining an image whose color information and tone information are limited, the user may want to acquire object information more precisely or increase the degree of freedom of adjustment in image editing. For these reasons, a demand has arisen for acquiring an image with larger amounts of color information and tone information.
To meet this demand, there is a technique for acquiring a larger amount of color information by performing shooting using a monochrome camera a plurality of times while switching a plurality of color filters having different spectral transmission characteristics (for example, S. Tominaga, “Spectral imaging by a multi-channel camera”, Journal of Electronic Imaging, Vol. 8, No. 4, pp. 332-341, October, 1999). Note that the thus-obtained image having a large amount of color information will be called a multi-band image.
There is also a technique of acquiring information of a dynamic range wider than the limit of a capturing device by performing shooting a plurality of times while changing the exposure (for example, literature 1: Paul E. Debevec et al., “Recovering high dynamic range radiance maps from photographs”, ACM SIGGRAPH 2008 classes, Aug. 11-15, 2008). A technique of compositing a plurality of obtained images into one image having a wide dynamic range will be called high dynamic range composition.
However, the above techniques require a plurality of times of shooting operations cumbersomely, and cannot cope with a moving object.
To the contrary, Japanese Patent Laid-Open No. 2009-278577 (literature 2) discloses a technique of preparing cameras for respective colors to be acquired, and after capturing, integrating images captured by these cameras to obtain a color image. This technique requires a plurality of cameras for acquiring color information, but can acquire a multi-band image. Japanese Patent Laid-Open No. 2002-171430 (literature 3) discloses a method of preparing a plurality of cameras different in sensitivity characteristic, and after capturing, performing high dynamic range composition for images captured by these cameras.
The techniques disclosed in literatures 2 and 3 require alignment between images when integrating images captured by a plurality of cameras. However, a plurality of images to be aligned are captured by cameras different in color or sensitivity characteristic, so high alignment accuracy cannot be obtained.